This invention relates to steering systems of automotive vehicles and more particularly to a method and device for controlling to steer rear wheels of a four-wheel steering system of an automotive vehicle (hereinafter referred to as vehicle).
There have been proposed and developed four-wheel steering systems of vehicles of the type wherein a reference value of the rear-wheel steering angle is determined from the steering angle of the steering wheel and the vehicle speed, and the rear wheels are steered in accordance with this reference value. In these four-wheel steering systems, there is one wherein means for detecting the steering angular speed of the steering wheel is provided, and thus a reference value of the rear-wheel steering speed is determined in accordance with the steering angular speed. Then, by steering the rear-wheel at the speed of this reference value, rear-wheel steering without response delay can be realized. One example of this steering system is disclosed in Japanese Patent Laid-Open Publication No. 149562/1987.
According to the prior art like this, in a range of low and high vehicle speeds, the rear wheels are steered in reverse-phase (opposite) direction relative to the front wheels so as to improve the turning ability. And, in a range of high vehicle speed, the rear wheels are steered in the coincident-phase direction same as the front wheels thereof in order to secure safety drive. In this case being provided, a device for controlling the rear-wheel steering speed in proportion to the steering wheel angular speed and being reduced the response delay of the rear wheels, the following problem arises. That is, when the rear wheels are abruptly steered in the reverse-phase direction in order to avoid a danger or a critical situation as a corrective steering manipulation during driving at low or medium speed in an abnormal state, control becomes difficult by the low convergence of the wheel movements.